What Are Postbiotics and What Do They Have to Do With Gut Health?
Gut health is an enormous topic that just got even bigger.
You know about probiotics: bacteria that provide benefits to our gut, metabolic, and/or overall health when eaten. Some probiotic bacteria colonize our guts—they take up residence in our digestive tract and provide lasting effects. Some probiotic bacteria are transients—they visit and impart benefits and interact with our guts and its inhabitants, but do not stay.
You also know about prebiotics: non-digestible food components that nourish and provide food for the bacteria living in our guts. Prebiotics include fermentable plant fibers, resistant starch, “animal fiber,” and certain polyphenols.
This is standard stuff. Entire store shelves are devoted to fermented dairy, pickles, sauerkraut, supplements, kombucha, and other sources of probiotics. You’ve probably got all sorts of strange gums and fibers and powders that serve as prebiotic substrate for gut bugs. Gut health is mainstream.
But you probably don’t know about postbiotics.
What Are Postbiotics?
Postbiotics are the products created by our gut bacteria after they consume prebiotics, interact with incoming food components, and interact with other bacteria. They include:
- Short-chain fatty acids like butyrate, propionate, and acetate
- Vitamins like inositol, vitamin K2, and certain B vitamins
- Neurotransmitters like GABA and serotonin
And then there are the likely innumerable postbiotic effects, metabolites, and outcomes that we have yet to elucidate and quantify.
In other words, postbiotics—the actions, products, and interactions of probiotic bacteria—are the entire reason we’re so interested in probiotics and prebiotics.
Short Chain Fatty Acids
The short chain fatty acids that are byproducts of fiber fermentation, including butyrate, propionate, and acetate, improve our health in many ways. Butyrate in particular has been shown to have beneficial effects on insulin sensitivity, colonic transport, inflammation, and symptoms of Crohn’s disease.123 It’s also the preferred fuel source for our native colonic cells, so without enough butyrate, our colonic cells can wither and die off, leading to digestive impairments and even cancer. Mucin-degrading bacteria predominate in colorectal cancer patients, for example, while butyrate-producing bacteria dominate in healthy patients without cancer.4 Populations with lower rates of colorectal cancer also tend to have higher levels of butyrate.5
Propionate is helpful, too, reducing fat storage and improving lipids.6 One of the coolest effects though is on exercise tolerance: certain gut bacteria have been shown to metabolize lactate into propionate, and in doing so improve exercise capacity. In fact, elite athletes tend to have higher levels of propionate-producing bacteria in their guts.7
Acetate is less well-characterized, but it has been shown to enhance butyrate production.
When gut bacteria consume substrates, they produce various metabolites, the most famous of which are the short chain fatty acids butyrate, acetate, and propionate discussed in the previous section. But they also produce vitamins in the process, particularly vitamin K, B-vitamins, and inositol.8
Although this hasn’t been directly quantified, we know the potential for gut bacteria that produce vitamin K2 exists. Broad spectrum antibiotic usage leads to lower levels of vitamin K2 in the human liver, a consequence that only makes sense if the antibiotics are killing vitamin K2-producing bacteria.9 What we do make in the gut can absolutely be absorbed and utilized.10
And gene sequencing of bacterial strains known to inhabit human guts has found strong evidence of genetic capacities for the manufacture of folate and other B-vitamins. However, these vitamin producing genes are only expressed “when bifidobacteria are in their natural ecological niche.”11 You can’t eat a diet of processed junk food and refined grains and hope to nourish the relevant bacteria. If you want your gut bacteria to produce vitamins as postbiotics, you need to provide their “natural ecological niche”—prebiotics, good sleep, healthy living, colorful plants, sunlight and exercise.
Certain gut bacteria can actually turn phytic acid into inositol, preventing the mineral-binding activity of the phytic acid and unlocking the mood regulation and insulin sensitizing effects of inositol.12 The more phytate-rich foods you eat, the better your gut bacteria get at breaking it down into inositol.13
When scientists first discovered the enteric nervous system, housed in the vagus nerve and running from the gut to the brain and back again, they assumed it only delivered information and instructions about digestive contractions. But now we know that it’s much more than that. We know that the gut bacteria produce 95% of our serotonin, half of our dopamine, and a significant portion of our GABA.14 This may explain why unhealthy gut biomes are strongly linked to mental health issues like depression and anxiety, and it’s probably why we even have the concept of a “gut feeling.”
People with major depressive disorder are more likely to have low levels of Bacteroides, a bacterial genus known for producing large amounts of GABA in human guts.15
Should You Take Postbiotic Supplements?
Some companies have begun releasing postbiotic supplements, like straight-up sodium butyrate and something called “yeast fermentate,” which is the concentrated extract of a brewer’s yeast fermentation. The butyrate and fermentate are probably fine to take, but that’s not the best way to get postbiotics. It’s not the same as letting your gut bacteria make it themselves.
I say this all the time regarding probiotics and prebiotics: rather than fixate on a single strain, single metabolite, single short-chain fatty acid, or single specific fiber source, think in terms of whole foods, whole patterns of lifestyle and health. There’s so much we don’t know about what’s going on in our gut—up to 65% of the bacteria living in our guts hasn’t even been cultured and analyzed—and it’s silly to think we can engineer specific outcomes. For instance, you can’t just megadose with propionate and hope to get performance boosts in the gym or choke down butyrate and drop your insulin resistance. It may work, but it probably works better to come at the situation with a bottoms-up approach that emulates or is the natural, organic path than to insert some ingredient midway through the process.
That said, perhaps postbiotic supplementation will improve down the line.
How Do You Support Natural Postbiotic Production?
That’s a big question, but there are answers.
Eat prebiotics. This post gives a good overview of prebiotics and how to get them. And read up on resistant starch, a particularly pro-butyrate form of prebiotic. Excellent sources of prebiotics include onions, garlic, leeks, Jersualem artichokes, asparagus, slightly green bananas, cooked and cooled potatoes, pistachios and almonds, chicory root, mushrooms, dandelion greens, and carrots. I could go on, and those listed are most of the most potent sources, but you get the point—plants contain prebiotics.
- Eat probiotics. Eat fermented dairy, eat fermented vegetables, take supplements if that’s easier or if you wish to supplement.
- Eat colorful fruits and vegetables and animals. These plant pigments, polyphenols, and animal connective tissues are prebiotic substrate for the gut bacteria.
- Maintain good circadian hygiene. Sleep and circadian rhythm affect every system in the body, and the gut is no different.
- Manage stress. Stress disrupts gut bacteria and worsens gut health.
- Play in the dirt. Spend time outside getting dirty.
- Get sun. Sunlight is another underrated modulator of gut bacteria diversity.
- Eat whole foods. Whole foods contain the broad spectrum of food components, many of which we haven’t quantified and some of which will have positive postbiotic effects on the gut bacteria.
For a comprehensive treatment of all the things that affect gut bacteria in both positive and negative ways, read this post.
As you can see, nothing is laid out with great specificity (“to produce [this specific postbiotic], do [this specific intervention] or take [this specific supplement]”). You can’t just do one thing. You have to take a comprehensive, holistic, Primal approach. But here’s the great thing about doing it that way: you won’t just get the benefits of postbiotics, but also the health, fitness, and overall happiness benefits of living more healthfully in general.
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